The first thing you should know about Sierra Nevada water is that it is among the best anywhere. We have very tasty water here in Hawaii, but, last year, when I returned from three weeks on the trail, I found it almost undrinkable. I had become spoiled drinking from streams and lakes, instead of from the tap.
Sierra Nevada water is so good that some claim to never purify their water while on the trail. Of course, they always follow that up with a comment along the line of: “as long as you are careful about where you drink.”
When you try to nail someone down on the subject of what sources are safe, after a series of questions, you come to realize the answer is, “Where the water isn’t contaminated.” Talk about begging the question.
My position has always been that you should purify the water you drink on the trail, unless it comes from a tap (like at Sunrise Camp), or directly from a spring. There are number of technologies available to do that.
The trouble, of course, with “technologies” is that they are not foolproof. Even a simple filter, which is about as low-tech as you can get, can become lost. If you are FORCED to drink untreated water, where should you get it?
Here are some tips courtesy of Dr. Robert Derlet, co-author of a study called, “Coliform Bacteria in Sierra Nevada Wilderness Lakes and Streams: What is the Impact of Backpackers, Pack Animals, and Cattle?”
Side streams, without stock or cattle upstream, are the preferred sources. Also good are the top six inches of calm water (no waves caused by wind or agitation) in a sun baked lake. As he points out, ultraviolet light is a wonderful disinfectant.
The areas to avoid are anywhere cattle or horses have grazed. Also, regardless of how you are collecting your water, do not disturb any algae near the bottom; algae contains millions of microorganisms.
This is good information, but remember this: even where there is no stock or cattle, there is wildlife. Bear scat or a decaying deer carcass can be just as problematic. If you want to be sure, purify!
More on water purification can be found here.
Good hiking, Ray
Note: Special thanks to John Ladd of the John Muir Trail Yahoo Group and Dr. Robert Derlet